This invention relates generally to improvements in multitrack audio recording and playback systems and, more particularly, to a new and improved method and apparatus for recording multitrack audio from a multitrack audiotape onto multiple laser videodiscs for playback from multiple laser videodisc players. Recording the audio onto laser videodiscs allows for the exploitation of several of the advantages of laser videodisc technology, including the increased durability of laser videodiscs over audiotapes and the higher reliability and reduced maintenance of laser videodisc players over audiotape machines.
Multitrack audiotape machines are presently used to provide synchronized audio for animated and theater shows at some amusement parks. Some of the multiple tracks are used to carry wide bandwidth audio, such as music, and other tracks are used to carry narrow bandwidth audio, such as narration and sound effects. These multiple tracks are automatically synchronized to each other by virtue of their parallel placement on the same audiotape, and are synchronized to the various film projectors, animated characters, and other show elements by time codes recorded on one of the audio tracks. The multitrack audiotape machines are well suited for shows requiring more than about sixteen tracks, but because these machines are generally very costly and have poor reliability and high maintenance requirements, they are not well suited for smaller shows requiring a lesser number of tracks. Furthermore, such audiotape machines have no random access capability and the audiotapes typically wear out or degrade in quality with time.
Synchronized audio could be provided for these smaller shows by recording the multiple audio tracks onto multiple laser videodiscs. For example, a pair of channels of the wide bandwidth audio and a pair of channels of the narrow bandwidth audio could be recorded together on a single laser videodisc, with the two channels of wide bandwidth audio encoded in a video format on the laser videodisc. Such a laser videodisc would be created for each group of four channels from the multitrack audiotape. Multiple laser videodisc players would then be used to play back the multiple laser videodiscs, with the players synchronized to each other through their conventional gen-lock capability.
The laser videodisc approach has several advantages. Laser videodiscs do not wear out or degrade in quality with time as audiotapes do. The laser videodisc players are almost maintenance free and are highly reliable. Also, the laser videodisc players are much less expensive than the multitrack audiotape machines, and have random access capability, as well. Furthermore, the failure of one laser videodisc player will not cause the entire show to be interrupted.
The multiple laser videodiscs are created by first recording the groups of four channels from the multitrack audiotape onto a master multitrack audiotape. The groups of four channels are then recorded onto a master videotape, which is subsequently used to create a master laser videodisc for producing the multiple laser videodiscs. However, recording the audio from the master multitrack audiotape onto the master videotape requires multiple passes of the master multitrack audiotape. During each pass of the master multitrack audiotape, the master audiotape machine must be accurately synchronized to the videotape recorder. If the machines are not synchronized, the laser videodiscs that are later made from the master videotape will be unable to be accurately synchronized with each other during playback. Synchronizing a multitrack audiotape machine with a videotape recorder using typical SMPTE (Society of Motion Pictures and Television Engineers) timecode recorded on one of the audio tracks and prior art synchronizing equipment has provided a phase accuracy of approximately one hundredth of an SMPTE frame (one frame=1/30 second), or approximately 1800 degrees of phase error (5 cycles) at 15 KHz, between the two machines. This is not acceptable for multitrack stereo playback, or for sound that is panned from track to track, which requires a phase error of no more than about 20 degrees.
Accordingly, there has been a long existing need in the recording arts for a method and an apparatus for more accurately synchronizing a multitrack audiotape machine with a videotape recorder. The present invention clearly fulfills that need.